This invention relates to digital electronic recording and, in particular, to disk drive recording systems. More precisely, the invention relates to a disk drive having a rotatable actuator arm for positioning a magnetic recording head over the tracks of a disk.
A rotary actuator assembly of a hard disk file includes one or more actuator arms which are supported at one end and carry a transducer at the opposite (free) end. In order to move the transducer from track to track on a disk surface, the height of the actuator arm must be small enough to pass between two closely spaced magnetic disks.
The height between disks (assuming the recording disks are positioned horizontally) in a multiple-disk file is very limited. For this reason, an actuator arm must have a low profile from top to bottom. For example, FIG. 1 shows a side elevational view of the prior art actuator arm 10 disclosed in Riggle et al. U.S. Pat. No. 4,346,416. This actuator arm 10 has a relatively low height, compared to the width of the arm shown in FIG. 2.
Actuator arms used with rotary actuators must have sufficient stiffness in the directions of yaw, bending and torsion. "Yaw" motion is defined as deflection in a direction parallel to the disk surface. "Bending" motion is defined as deflection in a direction normal to the disk surface. "Torsional" motion for purposes of this disclosure is defined as a twisting motion about a central longitudinal axis 24 of the actuator arm (shown in FIGS. 1 and 2). The central axis 24 extends from a point central to the supported end 20 to a point central to the opposite, or free end 22. By providing sufficient stiffness in each of the above mentioned directions, vibration in the actuator arm is reduced, allowing the attached transducer to more quickly access data on the disk surface.
Improvements have been made to increase the stiffness in the directions of yaw and bending by providing actuator arms having upper, lower, and side surfaces which taper inwardly (converge) toward the central longitudinal axis from the attached end 20 to the free end 22.
A side elevational view of such a prior art actuator arm as disclosed in Riggle et al. U.S. Pat. No. 4,346,416 is shown in FIG. 1. The actuator arm has a pair of side surfaces 16 and 18 (shown in FIG. 2) which are wider at the attached end 20 than at the free end 22, and which taper inwardly (converge) toward a central longitudinal axis 24 extending from a point central to the attached end 20 to a point central to the free end 22.
The tapered side surfaces 16 and 18 provide improved yaw stiffness, as compared to substantially rectangular shaped side surfaces (not shown). Because the side surfaces 16 and 18 are tapered, the actuator arms of the prior art are also thicker from the upper surface 12 to the lower surface 14 at the attached end 20 as compared to the free end 22.
Although the actuator arm is thicker near the attached end 20 than at the opposite end 22, the prior art actuator arm 10 is the same thickness at the center as at the side surfaces 16 and 18, when each of the measuring points are located on a plane perpendicular to the central longitudinal axis 24.
A top plan view of the same prior art actuator arm is shown in FIG. 2. The prior art actuator arm 10 also includes a tapered upper surface 12, and a tapered lower surface 14 (shown in FIG. 1). Each surface 12 and 14 is wider at the supported end 20 than at the free end 22. Each surface 12 and 14 tapers inwardly (converges) toward the central longitudinal axis 24 from the supported end 20 toward the free end 22. Because of the tapered shape of surfaces 12 and 14, the free (opposite) end has a smaller width from side to side than the width of the attached end 20. The tapered surfaces 12 and 14 provide improved bending stiffness to the arm 10, as compared to untapered, substantially rectangular surfaces (not shown).
Because the four exterior surfaces 12, 14, 16, and 18 are each tapered, the mass of the prior art actuator arm is more concentrated near the supported end 20 of the actuator arm 10 than at the free end 22. An actuator arm having more of the mass concentrated at the supported end has a lower mass moment of inertia as compared to an actuator arm having less than four tapered surfaces. An actuator arm with a lower mass moment of inertia is capable of more rapid acceleration, which allows the disk drive to read and write data more rapidly. The mass moment of inertia of the prior art actuator arm is further reduced by reducing the mass of the arm with a series of cut-outs 30 which define side support members 32 and 34.
Although the prior art actuator arms have attempted to provide adequate stiffness in the directions of yaw and bending, these actuator arms do not have the maximum degree of stiffness possible for the given space limitations. In addition, the prior art actuator arm is not sufficiently resistant to torsional bending, which is known to have a negative effect on disk drive performance. Torsional bending, for example, is known to cause instability in the operation of the transducers.
Actuator arms with adequate stiffness in each direction of bending, torsion and yaw have a relatively high resonant frequency in each direction. If the resonant frequency is too low, large amplitude motions can be excited, causing read/write or servo errors.
The prior art actuator arm structure shown in FIGS. 1 and 2 does not achieve the maximum stiffness possible in the directions of bending, yaw and torsion for the given space limitations.